Chapter 9

Designing Systems for Diverse Environments

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Learning Objectives To gain an appreciation of the diversity

of design and development environments faced by the modern analyst

To understand the advantages and disadvantages of centralized versus distributed data systems

To learn the differences between the file server and the client–server approaches to networking

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Learning Objectives To explore the common network

topologies and understand their relative advantages and disadvantages

To gain an appreciation for development issues within ERP, collaborative, intranet, and data warehousing environments

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Application Development Environment

Central computing environment Single processor Clustered approach

Distributed computing environment LAN/WAN Internet/WWW

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Figure 9-1. Typical Clustered Central Computing System

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The Distributed IS Some subsystems…

Need to interact with other subsystems

Need to share files with other subsystems

Require little interaction with other subsystems

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Figure 9-2. Typical Distributed Computer System

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The Distributed IS Reliability

A particular piece of data is available at a given time regardless of the location of the user

Survivability System’s ability to continue to

provide service to its users despite the failure of one or more nodes

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The Drive to Distribute The cost of PCs is dropping rapidly. The interface and computing power of

such devices is increasing. Increased communications bandwidth and

inexpensive storage costs The demand for locally specific

applications is rising. The Internet and the WWW provide a

natural connectivity vehicle to access data and applications from around the globe.

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Table 9-1. Comparative Pros and Cons of Distributed Computing

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Types of Distribution Distributed System

Distributed Applications Distributed Data

Hardware Architecture File Server Client Server

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Distributed Applications Allowing geographically dispersed end

users to access and use a variety of software applications

Applications can be stored in a single location and accessed by any processor connected to the system

A single application can be replicated to multiple locations throughout the network

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Distributed Data Data can be either replicated

across multiple sites for ease of access or

Partitioned such that a portion of the data resides in several locations throughout the network

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File Server versus Client Server Approach File Server

Manages the various file operations associated with the system and can be thought of as an additional hard dive for each workstation

Client Server Processing load for an application is

divided between the workstation and the server

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Figure 9-3. Typical LAN/WAN Connectivity

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Figure 9-4. Comparison of File Server and Client/Server Approach

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Connectivity Diagram Location Connectivity Diagram

(LCD) Depicts the shape of a network in

terms of the location of the various components on the network

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Symbol Description

Specific Location: anyplace where end users exist to use or interact with the information system or application or where business can be conducted and work performed.

Cluster Location: a group of end users who perform the same duties in the same logical or physical location.

Mobile Location: one or more end users who typical perform their work in multiple locations (i.e. sales representatives).

External Location: organizations and agents outside of the company but that interact with or use the information system.

Table 9-2. Symbology for Location Connectivity Diagrams

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Figure 9-5. Example of a Location Connectivity Diagram

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Connection Topologies Bus Topology

Ethernet Ring Topology

Token Ring Star Topology

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Picture of original drawing by Robert Metcalfe of the conceptualization of Ethernet

Ethernet

Works tation Mac Classic

Laptop computer

IBM AS/400

IBM la s e r p ri n te r

Figure 9-6. Typical Bus Network Topology

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Token Ring

Work s tation

Work s tation

Work s tation

Work s tation

Work s tation

Work s tation

Work s tation

IBM AS/400

Figure 9-7. Typical Token-Ring Network Topology

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IBM Compatib le

IBM Compatib le IBM Compatib le

IBM Compatib le

IBM Compatib le

IBM Compatib le

IBM Compatib le

IBM Compatib le

Figure 9-8. Typical Star Network Topology

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Topology Advantages Disadvantages Star

- Low complexity with regard to network management - Failure of a node does not disable the network

- Requires significantly more cabling than alternatives - Failure of the central server disables entire network - Throughput can be slowed due to large volumes of requests at the central server

Ring - Relatively easy to synchronize network connections - Can span greater distances since message is regenerated at each node - Generally high bandwidths can be achieved

- Entire network is disabled if any cable is cut or experiences fault - Relatively high installation costs

Bus - Low cabling requirements - Relatively inexpensive to install

- All or part of the network may be disable is cable is cut or experiences fault

Table 9-3. Comparative Advantages and Disadvantages of Common Network Topologies

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Managing Distributed Data Data Replication

Create a copy of each of the databases contained in the system at each workstation

Provide users with high reliability of access to the data

Storage requirements are significantly increased

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Managing Distributed Data Data Partitioning

Partition the data using some logical approach such that the contention for data across workstations is minimized

Location transparency Horizontal partitioning Vertical partitioning

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Figure 9-9. Lotus Notes Database Replication Control Screen

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Table 9-4. Comparative Advantages and Disadvantages of Data Distribution Methods

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Design for Distributed Systems Distributed systems characteristics

A large number of interconnected machines Open (heterogeneous) hardware and

software systems Complete autonomy over hardware and

software resources Dynamic system configuration and

integration Time-sensitivity of the expected solution

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Traditional Design Environment

Distributed Design Environment

Local Remote Sequential Concurrent

Homogenous environment Diverse environment

Fixed Location Mobile

Single copy Multiple copies

Synchronous Asynchronous Direct Indirect

Shared Separate

Global Context relative

Complete Failures Partial failures

Early binding Late binding

Global system time Diverse local times

Single view Multiple views

Table 9-5. Traditional Design Assumptions versus Distributed Design Assumptions

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Design for Distributed Systems Challenges

Separation Diversity Federalism Concurrency

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Design for Collaboration The system should support

individual works as well as collaboration.

The system must afford mutual intelligibility.

The system must support simultaneous access.

Collaborative wearable computers

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Figure 9-12. Screenshot of Collaborative Work Environment

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Figure 9-13. Examples of Currently Available Wearable Computing Devices

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Designing for Enterprise Resource Planning

ERP Features ERP systems are installed on a typical

DBMS Require initial setup according to the

organization’s process ERP system includes reporting tools

for main and ad hoc reporting

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Typical Nonintegrated Organizational IS Organizational ERP System

Marketing, Resource Planning, Accounting,

Finance, Manufacturing, Human

Resources, Sales, Suppliers, Customers,

Marketing Database

Human Resources Database

Materials Database

Accounting Database

HR Applications

Manufacturing Applications

Financial Applications

Marketing and Sales

Applications

HR Applications

Manufacturing Applications

Financial Applications

Marketing and Sales

Applications

Figure 9-14. Comparison of Typical Organization IS with ERP Approach

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ERP Implementation Comprehensive Implementation

Focus on business improvement rather than on technical improvement

Compact Implementation Focus on making the technical

migration to the ERP

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Designing for Intranets Focus on tasks rather than

documents for simple data capture Aim to integrate those tasks into

distinct processes Encourage collaboration by

creating shared and familiar spaces

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Intranet Design Myths Intranets are cheap Build it and they will come Intranets are for really big

organizations Intranets requires an Internet

connection and are not secure Intranet are low maintenance

applications Intranets are an IS thing

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Designing for the Data Warehouse

Assumptions DW is physically separated from all

other operational systems DW holds aggregated data and

transactional data for management separate from those used for on-line transaction processing

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Table 9-6. Operational Data Store and Data Warehouse Characteristics

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Data Directory Functions

Process Management

Data Directory

Application Messaging Layer

Figure 9-17. Components of the Data Warehouse Architecture

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Data Warehouse Topology Virtual or point-to-point Central Distributed

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DW Implementation Seven Deadly Sins

If you build it, they will come Omission of an architectural

framework Underestimating the importance of

documenting assumption Failure to use the right tool for the job

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DW Implementation Seven Deadly Sins (continued)

Life cycle abuse Ignorance concerning the resolution

of data conflicts Failure to learn from mistakes

- End -

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Chapter Summary This chapter established the range

of diverse environments you can expect to encounter during your career.

Despite the diversity of the environments, the basic tenets and foundations of good system design and development still prevail.

Chapter 9

End of Chapter